Hi Christophe, our mails overlapped :)
> PicoLisp was not the Haynes one, but the one referred as «Newlib» here: > http://en.wikipedia.org/wiki/Linear_congruential_generator#Parameters_in_common_use Right. I took it originally from the book by Donald Knuth. > Maybe I was too tired. The difference is 33, and we see in the Ersatz src: > n = (int)(Seed >>> 33) % n; Right. > What I don't understand is why Ersatz shifts by 33, and PicoLisp by BITS, > (which should IMHO be 32). True. In fact, as I wrote, I don't remember that either. Perhaps a sign issue? Would it make sense to change it? Should be well tested though. This connects to my next remarks/questions: > * The Wikipedia page mentions taking «bits 63...32». I guess that > they start at bit 0, thus should the shift be 32 ? Knuth writes that the highest bits are more random than the lower bits in a linear congruential generator. > * Is 33 used because of the sign bit ? Yes, perhaps. > * In the PicoLisp src, why use LL and not ULL to define > 6364136223846793005? : (hex 6364136223846793005) -> "5851F42D4C957F2D" As you see, this number doesn't have its sign bit set in 64-bit two-complement representation (it would be 8 or higher in its most siginificant digit). So "unsigned" makes no difference. ♪♫ Alex -- UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe
